Gap junctions contain intercellular channels that are critical for cardiac electrical conduction and cardiovascular cell coupling. Abnormalities of the abundance, distribution, or sequences of subunit gap junction proteins (connexins) within the cardiovascular system have been associated with severe cardiac arrhythmias, developmental abnormalities, or atherosclerosis in humans or in mice. Connexins may have relatively specialized functions within the cardiovascular system, since they have differing patterns of expression, and they form channels with differing conductance and selectivities. Preliminary data suggest that there is a significant prevalence of different polymorphic variants of cardiovascular connexins which may form channels which vary in conductance. The present proposal will address issues that determine the extent of gap junction mediated coupling between cardiovascular cells: (1) regulation of connexin expression (i.e. when and where is a connexin expressed?) and (2) conductance and permeability of connexin channels (i.e. what can go through the channel?). Specifically, we will ask: What determines the limited expression patterns of two specialized cardiovascular connexins (Cx37 and Cx40)? What is the extent of natural variation of cardiovascular connexin sequences; what is the prevalence of different polymorphic variants; are they associated with clinical disease; and, do they exhibit altered channel function? What sequence features determine the molecular permeability of connexin channels? We will use a variety of molecular tools to analyze the promoters for Cx37 and Cx40 in vitro and in vivo. We will use PCR amplification of genomic DNA from a population of patients to screen for connexin polymorphisms. We will study the conductance and permeability properties of the wild-type and polymorphic or mutated connexins as expressed in Xenopus oocytes and in transfected cells and as reconstituted in liposomes. This study may have significant implications for the elucidation of cardiovascular disease (including arrhythmias) associated with connexins.